In plasma processing applications arcs are known to develop when a discharge occurs between a point on a cathode where charge has accumulated and a point on the anode. If not extinguished quickly, arcs can be very detrimental to the process and the quality of the processed film.
Past approaches to arc control in plasma processes have focused upon the reduction of energy supplied by a power supply into an arc. In some power supplies, arcs are extinguished by turning off after the arc is detected. In variations of these past approaches, a shunt switch is placed across the power supply and is used to circulate inductor current inside of the power supply, and when the arc is extinguished, the shunt switch opens. These types of systems are effective to some extent, but are unable to provide the expedient arc mitigation often necessary in present processing environments.
In some systems, a second-power supply is employed, so that during an arc event, power from the first-power supply is removed from the plasma chamber and power from the second-power supply is provided to the plasma chamber with a reverse polarity of the first-power supply. Although, these systems enable arcs to be extinguished relatively quickly, the second-power supply adds substantial cost to the system in substantially increases a risk of failure.
Another approach that has proven to be effective in plasma processing applications (e.g., where relatively low power and low current is utilized) includes employing a tapped inductor in series with an output of a power supply and a shunt switch. The tapped inductor acts as an autotransformer and provides a reverse voltage that is a function of the turn ratio of the tapped inductor. Tapped inductors that can handle higher currents and provide the desired low-leakage inductance, however, are relatively expensive. And implementing cable with a sufficiently low inductance is also costly-especially at higher currents.
As process currents increase, one of the biggest problems in dealing with arc energy is the energy stored in the output cable, which is proportional to the square of the current carried by the cable. Problematically, this stored energy is not controllable by the power supply and the only path available to current generated from the stored energy is into the arc. As a consequence, the current from the stored energy may actually extend the life of the arc and add to the damage (e.g., to the work piece and/or chamber) caused by the arc. And cable designs that minimize stored energy (e.g., by minimizing an inductance of the cable), can quickly become costly and impractical to build when balancing such constraints as length, insulation, wire size, and cost.
Although present devices are functional for many applications, they are not sufficient for many implementations or are otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.